Carbide and nitride ternary ceramic glove and condom formers

ABSTRACT

A slip-casted article former containing ternary ceramics, particularly of carbide and nitride materials, having the formula M.sub.n+1AX.sub.n (MAX), where M is a transition metal, A is an element from Groups IIIA and IVA of the periodic table, X is nitrogen or carbon and n is 1, 2, or 3. The ternary ceramic article may be a glove or condom former. A process for making a ternary ceramic article employing a slip cast method.

This application is the National Stage of International Application No.PCT/US02/40113, filed Dec. 16, 2002, which claims the benefit of U.S.Provisional Application No. 60/341,892, filed Dec. 18, 2001.

FIELD OF THE INVENTION

The invention is directed to articles containing ternary ceramicmaterial and a method of making the articles.

BACKGROUND OF THE INVENTION

Formers are rigid molds sized and shaped to define the dimensions of thefinished products. Formers are employed in the manufacture of latex andsynthetic polymer products, such as examination and surgical gloves andcondoms. The formers are typically made of wood, ceramic, glass,porcelain, plastic, steel or aluminum and are dipped, usually fingersfirst in the case of a glove former, into a liquid latex bath, includingadmixed chemicals, where the latex adheres to the former. The glove orcondom formers may be heated prior to beginning the dipping process.Glove and condom formers are usually pre-coated with a coagulant to gelthe latex and to facilitate removal of the article from the former.Typical coagulants include calcium nitrate. Additional dips in latexbaths that contain fillers may also be required. The latex is coagulatedand the glove or condom is released from the former usually by peelingthe glove or condom from the former. The articles may be removed fromthe former in water. The gloves or condoms may also go through leachingand washing cycles to remove residual chemicals before being strippedfrom the former. The finished articles are then removed from the formersuch that the outer layer from the former will be the innermost layer ofthe glove or condom. The articles may then be packaged and sterilizedfor shipping.

After repeated cycles of chemical dips, formers begin to degrade andmust be replaced. As a benchmark for durability, porcelain formersremain in good condition for up to two weeks when exposed to aconcentrated solution of potassium hydroxide.

Ternary ceramics are generally known to be hard or brittle and notsuitable for use in the manufacture of machined parts. However, titaniumsilicon carbide Ti₃SiC₂ has been synthesized to result in a soft,machinable, strong and lightweight material. Ti₃SiC₂ is anomalously softfor carbide materials. Single-phase samples of the material werecharacterized for thermal stability and oxidation-resistance. Samplebars of Ti₃SiC₂ material were quenched in a pail of water from 1,400° C.and found to have a slightly increased strength after quenching. Samplesof Ti₃SiC₂ materials are also surprisingly machinable. Ceramics aretypically too brittle to be machined, however, after drilling throughthe initial hard crust of the Ti₃SiC₂ the samples were found to benearly as machinable as graphite.

Ti₃SiC₂ has properties of both metals and ceramics. Like a metal, it ismachinable, thermally and electrically conductive, resistant to thermalshock and plastic at elevated temperatures. Like a ceramic, it isrefractory (i.e., has a decomposition temperature of greater than 2,000°C.), oxidation-resistant, stiff and lightweight (roughly 4.5 grams percubic centimeter), its thermal expansion is relatively low, more like aceramic than a metal.

In slip casting, sometimes called drain casting, a plaster of paris moldis filled with a slip. Slip is a liquid containing a ceramic material ina water suspension. As the mold absorbs water, the ceramic suspensionsolidifies uniformly on the walls of the mold. Once the desired wallthickness is reached, the remaining slip is drained, the mold isseparated or broken, and the part is removed. The part is then sinteredin an oven.

WO 98/22244 describes a dense ceramic work piece made by pressing acombination of powdered Ti₃SiC₂ and a powdered material that is solublein the Ti₃SiC₂ into a green body. The green body is then heated underpressureless sintering conditions to a temperature above a point atwhich a liquid is formed but below the melting point of the mixture. WO98/22244 does not teach or disclose making hollow objects (like formers)with a plaster of paris mold and a liquid dispersion of powderedTi₃SiC₂.

Conventional formers that are typically made of wood, ceramic, glass,porcelain, plastic, steel or aluminum deteriorate after continualexposure to the heat and chemicals employed during the glove and condommaking process. Deterioration causes pitting in the formers, and thegloves and condoms produced from the pitted formers have pin hole sizeddefects. There is a need, therefore, for glove and condom formers of adurable material that will reduce the frequency with which the formersmust be replaced. It is desirable that the durable formers do nototherwise interfere with the quality of the glove or condom produced.

SUMMARY OF THE INVENTION

The invention is directed to an article, such as a former, containing aternary ceramic material having a chemical formula of M_(n+1)AX_(n),where M is an early transition metal, where A is an element selectedfrom the group consisting of Group IIIA elements and Group IVA elements,where X is selected from a group consisting of carbon, nitrogen andcombinations thereof, and where n is selected from a group consisting of1, 2, and 3; a binder; and a viscosity modifier.

Unlike previous formers, embodiments of the present invention lead to aformer made of a high strength, high temperature-stable material thatwithstands repeated chemical dips. Since the formers of the presentinvention are made with a more durable material than previous formers,the frequency with which the formers have to be replaced is greatlyreduced.

The invention is also directed to a method of making an article, such asa former, that includes the following steps:

(a) Mixing a ternary ceramic powder, water, a binder, and a viscositymodifying agent to form a dispersion;

(b) Pouring the dispersion of step (a) into a plaster of paris mold andallowing the dispersion in the plaster of paris mold to set for about 30minutes to about 5 hours;

(c) Pouring off any excess amount of the dispersion in the plaster ofparis mold;

(d) Allowing the dispersion in the plaster of paris mold to air dry forabout 1 hour to about 8 hours;

(e) Breaking open and remove the plaster of paris mold from a former;and

(f) Firing the former of step (e) in a furnace at a temperature fromabout 1000 to about 1500° C. for about 1 hour to about 8 hours.

DETAILED DESCRIPTION OF THE INVENTION

The articles of the present invention contain ternary ceramic material.The ternary ceramic material has a chemical formula of M_(n+1)AX_(n),where M is an early transition metal, where A is an element selectedfrom the group consisting of Group IIIA elements and Group IVA elements,where X is selected from a group consisting of carbon, nitrogen andcombinations thereof, and where n is selected from a group consisting of1, 2, and 3; a binder; and a viscosity modifier. Articles include, butare not limited to, formers such as glove and condom formers. The amountof the ternary ceramic material present in the article is about 100weight %, based on the total weight of the article.

A preferred ternary ceramic material is Ti₃SiC₂. Two compounds similarto Ti₃SiC₂ have been identified and synthesized. These compounds areTi₃GeC₂ and Ti₃AlC₂ where a single germanium or aluminum atom issubstituted for silicon. These compounds (Ti₃SiC₂, Ti₃GeC₂ and Ti₃AlC₂)are referred to as “312” compounds for the number of atoms of eachelement in the compound, respectively.

Chemically related compounds have a “211” or “413” formula. Thechemically-related 211 and 413 compounds are expected to havecharacteristics similar to the 312 compounds. The MAX phase ternarylayered compounds are generally defined, then, by the formula ofM_(n+2)AX_(n), where M is an early transition metal, A is an A-groupelement appearing generally in Groups IIIA or IVA of the period table ofchemical elements, X is carbon or nitrogen or both and n is 1, 2, or 3.

The 413 compounds include Ti₄AN₃, while the 211 compounds include thecompounds of Table 1.

TABLE 1 “211” Compounds Ti₂AlC Ti2AlN Hf₂PbC Cr₂GaC V₂AsC Ti₂InN Nb₂AlC(Nb,Ti)₂AlC Ti₂AlN_(1/2)C_(1/2) Nb₂GaC Nb₂AsC Zr₂InN Ti₂GeC Cr₂AlC Zr₂SCMo₂GaC Ti₂CdC Hf₂InN Zr₂SnC Ta₂AlC Ti₂SC Ta₂GaC Sc₂InC Hf₂SnN Hf₂SnCV₂AlC Nb₂SC Ti₂GaN Ti₂InC Ti₂TlC Ti₂SnC V₂PC Hf₂SC Cr₂GaN Zr₂InC Zr₂TlCNb₂SnC Nb₂PC Ti₂GaC V₂GaN Nb₂InC Hf₂TlC Zr₂PbC Ti₂PbC V₂GaC V₂GeC Hf₂InCZr₂TlN

The articles of the present invention are made by a method referred toin the industry as “slip casting”. A dispersion is formed by mixing aternary ceramic powder, water, a binder and a viscosity modifying agent.A preferred ternary ceramic material is powdered Ti₃SiC₂, available asMaxthal from Kantal AB of Sweden. The amount of the ternary ceramicpowder ranges from about 15 to about 83 weight %, based on the totalweight of the dispersion.

The amount of the water ranges from about 15 to about 75 weight %, basedon the total weight of the dispersion.

The binder and viscosity modifier are cellulose-based materials.Suitable binders include, but are not limited to, cellulose powder,cellulose derivatives, and combinations thereof. The binders are presentin an amount ranging from about 1 to about 20 weight %, preferably fromabout 5 to about 10 weight %, based on the total weight of thedispersion. Suitable viscosity modifiers include, but are not limitedto, carboxymethylcellulose, polyacrylate acid polymers, and combinationsthereof. The viscosity modifiers are present in an amount ranging fromabout 1 to about 5 weight %, preferably from about 1 to about 2 weight%, based on the total weight of the dispersion.

The dispersion may be from about 25 to about 85 weight % solids,preferably from about 80 to about 85 weight %, based on the total weightof the dispersion. The dispersion or slurry is referred to as the slip.

The dispersion is poured into a plaster of Paris (calcium sulfatehemihydrate) mold. The plaster of Paris mold conforms to the desiredshape and size of the former. The dispersion is allowed to stand in theplaster of Paris mold for a time sufficient to allow the dispersion tocoat the inside of the plaster of Paris mold. The amount of time thatthe dispersion is allowed to stand in the plaster of Paris mold isdirectly proportional to the desired thickness of the finished article.Accordingly, the longer the dispersion is allowed to stand in theplaster of Paris mold, the thicker the surfaces of the article.

The excess amount of dispersion is then poured off and the dispersion inthe plaster of Paris mold is allowed to air dry for about 30 minutes toabout 5 hours. The plaster of Paris mold is then broken open and removedfrom the article.

After the article is allowed to air dry for about to about 1 hour toabout 8 hours, the article is fired in an oven at temperatures rangingfrom about 1000° C. to about 1500° C. This firing or heating is referredto as the sintering step. The article is fired for about 1 hour to about8 hours. The firing burns off the water, the binders, and viscositymodifiers, leaving a article containing about 100% ternary ceramicmaterial.

The following example describes a preferred embodiment to illustrate theinvention. However, it is to be understood that the invention is notintended to be limited to the specific embodiment.

EXAMPLE 1

A ternary ceramic of Ti₃SiC₂ was slip cast and sintered to into a sizemedium examination glove former by dispersing 2355 grams Ti₃SiC₂ ceramicpowder available as Maxthal of Kanthal AB of Sweden in 525 ml wateralong with 120 grams Cellulose QP, available from Union Carbide Corp.,of Danbury, Conn. The slip was poured into a plaster of Paris mold andallowed to set for 15 minutes before the excess slip is drained. Theformer was removed from the mold and allowed to air dry for 1 hour.After drying, the former was heated in a non-continuous (batch) oven attemperatures up to 1400° C. for 15 hours.

A portion of the former was tested to determine the durability of theformer. A sample portion of the former was weighed and immersed in a 20%solution of potassium hydroxide at 170° F. The sample was removed every7 days, weighed, and placed back into the potassium hydroxide solution.The results are shown in Table 2.

TABLE 2 Time (days) Weight (grams) 0 14.204 7 14.204 14 14.204 21 14.20428 14.204 35 14.204 42 14.204 49 14.133At the end of eight weeks the former began to show a slight loss inweight. Standard porcelain formers are known to degrade after two weeksof exposure to potassium hydroxide as evidenced by pitting in the formerand by producing gloves that have pin hole sized defects in the gloves.

It should be understood that various changes and modifications to theembodiments described herein will be apparent to those skilled in theart. Such changes and modifications can be made without departing fromthe spirit and scope of the present invention and without demising theattendant advantages. It is, therefore, intended that such changes andmodifications be covered by the appended claims.

U.S. Patents, cited herein are hereby incorporated by reference to thesame extent as if each reference were individually and specificallyindicated to be incorporated by reference and were set forth in itsentirety herein.

1. A slip-cast article comprising a ternary ceramic material having a chemical formula of M_(n+1)AX_(n), where M is a transition metal, where A is an element selected from the group consisting of Group IIIA elements and Group IVA elements, where X is selected from the group consisting of carbon, nitrogen and combinations thereof, and where n is selected from the group consisting of 1, 2, and 3, the article in the shape of a hollow condom or glove former and being resistant to pitting after two weeks of exposure to potassium hydroxide.
 2. The article of claim 1, wherein the transition metal is selected from Ti, Nb, Zr, Hf, Cr, Ta, V, Mo, and Sc.
 3. The article of claim 1, wherein the Group IIIA and Group IVA element is selected from Al, Ge, Sn, Pb, Ga, Tl, and In.
 4. The slip-cast article of claim 2 wherein the ternary ceramic is Ti₃SiC₂.
 5. The slip-cast article of claim 4 wherein the ternary ceramic is present in an amount ranging from about 100 weight %, based on the total weight of the former.
 6. A hollow former comprising a ternary ceramic material having a chemical formula of M_(n+1)AX_(n), where M is a transition metal, where A is an element selected from the group consisting of Group IIIA elements and Group IVA elements, where X is selected from the group consisting of carbon, nitrogen and combinations thereof, and where n is selected from the group consisting of 1, 2, and 3, the hollow former in the shape of a glove or a condom, made by slip-casting and resistant to pitting after exposure to potassium hydroxide for two weeks.
 7. The former of claim 6, wherein the transition metal is selected from Ti, Nb, Zr, Hf, Cr, Ta, V, Mo, and Sc.
 8. The former of claim 6, wherein the Group IIIA and Group IVA element is selected from Al, Ge, Sn, Pb, Ga, Tl, and In.
 9. The former of claim 7 wherein the ternary ceramic is Ti₃SiC₂.
 10. The former of claim 9 wherein the ternary ceramic is present in an amount ranging from about 100 weight %, based on the total weight of the former. 